Here are a couple of helpful examples on building a C# .NET Core Generic Repo.
In these patterns you must pass the model (or table) to the repo. After working with this pattern and patterns that define the model in the repo, I prefer the latter. This way you have intellense in the repo to list all the models.
Sample 1: C# Core Repo code on MSDN by Sandeep Shekhawat
Sample 2: A Truly Generic Repository by Chris Pratt (not the guy from Guardians)